The invention relates to a steam-driven tow line winch, or a tow winch with apparatus for automatic tension regulation which comprises a pressure regulating valve in the live steam line of the steam winch.
Large sea-going vessels, especially tankers, are moored at their berth with mooring hawsers which on board of the vessel are fastened (spooled) on the drums of tow line winches.
Since as a result of the movements of the ship with respect to the mooring posts (bollards) on land, such as they occur due to changes in the state of loading, under the effect of the tides, in locks or due to swell, the hawsers can be loaded (subjected to stress or strain) to the breaking point, suitable overload safety devices must be provided on the steam winches. But it is also desirable that on removal of the load (stress or strain), the hawsers automatically become taut again.
Every conventional steam winch is suitable for keeping a hawser under tension automatically, i.e., to haul in the hawser when the tension diminishes and to pay out the hawser when the tension increases, without manipulation of the hunting valve. For this purpose, the hunting valve is set for "heaving", and this causes the winch to stop when the pull (tension) of the hawser has reached a level which just balances the steam pressure in the cylinders of the steam winch and thus corresponds to the full nominal tension (line pull).
If the tension (line pull) increases further, the winch at first remains stopped until at approximately double the pull (200% of the nominal tension (line pull)) the internal resistances in the steam engine and drive train have been overcome and the winch is stripped backwards (in reverse) against the steam pressure. The hawser now is paid out, although the hunting valve of the steam engine is set for "heaving".
If the tension (line pull) falls again, then the winch first stops and starts to heave in again only when the friction losses have been overcome and the pull (tension) of the hawser has dropped below the nominal value.
It is desired that in the warping operation the manually controlled steam winch performs at the full nominal tension (line pull), but that when the ship is moored this value is exceeded only little or not at all during the automatic pay out, in order to protect the winches and the hawsers. In order to realize these operating conditions, two different designs have been used in the past.
If a slight change in tension (line pull) is required to differentiate between hauling in and paying out of the hawsers, then, if at all possible, the tension (pull) of the hawser should be measured at the steam winch, that is to say at the drum, so that the effect of the efficiency of the winches is eliminated. Suitable load scales are available which transfer the measured value to the control mechanism, i.e., in the case of steam winches to the hunting valve, and thereby control the steam engine at constant tension (line pull) (German Pat. No. 1,231,400). Numerous tow line winches have been equipped with this type of automatic mechanism. But, since the load scale arranged at the drum has to be designed for large torques and forces, it is very expensive. Furthermore, additional elements (parts) are required in order to transmit the impulse of the load scale to the hunting valve while avoiding hunting (pendulum phenomena).
If the main consideration is the limiting of the maximum tension (line pull) during withdrawing (paying out) of the hawsers from the drum, while it suffices to carry out the hauling in with considerably less force, then another known design (German Pat. No. 1,237,754) is suitable, which is simpler and is being used in practice. In this case, during automatic operation a pressure control valve at the exhaust-steam pipe of the steam winch becomes active, which dams up the counter pressure (back pressure) in the cylinders to the extent that the differential pressure effective at the pistons amounts to approximately half of the pressure required for the nominal tension (line pull). The hauling in of the hawsers thus takes place with half the tension (line pull), while the paying out takes place approximately with the nominal tension (line pull) for which the steam winch is designed at manual control. This manner of operation of the (pressure) control valve is obtained by the fact that an adjusting piston acted upon (actuated) by the live steam forces the valve cone at the exhaust steam outlet against its seat. Since the valve cone has twice the area of the adjusting cone, the outlet remains closed as long as the counter pressure (back pressure) in the machine lies below half of the live steam pressure, but is opened when the counter pressure rises above half of the live steam pressure. The disadvantage of this type of design is that in automatic operation the differential pressure, and thereby the tension (line pull), changes when the live steam pressure fluctuates. A setting for different (selective) tensions (line pulls) is not possible, since the construction of the pressure control valve is meant only for a fixed ratio of live steam pressure to counter pressure.
Also known (German Pat. No. 1,124,652) is the installation of a pressure control valve in the live steam line of the winch and this pressure control valve keeps any arbitrarily set pressures in the steam engine constant. In order to prevent in the stopping position or when the hawsers are being pulled off (paid out) the pressure rising above the desired value caused by unavoidable leaks in the (pressure) control valve and by compression during backwards (reverse) turning of the steam engine, a relief valve is provided so that the steam can blow off to the exhaust steam line. In this arrangement, however, the setting of pressure control valve and relief valve to points of response which differ only little from each other, causes difficulties, and the condition is quite likely to occur in which steam flows off to the exhaust steam line when this is not desired at all.
The object of the present invention is to avoid the difficulties present in the known steam-driven tow line (mooring) winches and tow winches and to design the device for automatic tension (line pull) regulation in such a way that faulty response of the device is prevented with certainty and exhaust steam losses (wastes) are prevented at the same time.
According to the invention, this object finds its solution in the fact that the pressure control valve is equipped with a sleeve valve, the sleeve position (slide position) of which is controlled by means of the working pressure in the steam winch. The advantage obtained is that the control of the live steam pressure and the overflowing of steam to the exhaust steam line are both effected by the same device and thereby necessarily are made dependent on each other.
In a preferred embodiment of the invention, the pressure control valve (pressure regulator) has a sleeve valve which is acted upon from both sides and which is designed as a differential (pressure) piston, with the piston surface being acted upon by the live steam pressure exhibiting a smaller cross section than the opposite piston surface being acted upon by the working pressure in the winch. If a ratio of about 1:2 is selected for the cross sections of the piston surfaces of the sleeve valve, then the live steam passage to the hunting valve of the steam winch is completely open when the live steam pressure in the steam supply is more than twice as high than the working pressure in the steam winch. On the other hand, the passage to the hunting valve of the steam winch is completely closed when the live steam pressure lies below twice the value of the working pressure. The sleeve valve of the pressure control valve (pressure regulator) will automatically adjust itself to a position in which just the right amount of live steam is always released so that the working pressure is reduced to one half the live steam pressure.
The pressure control valve (pressure regulator) advantageously includes a passage to the exhaust steam line, which connects the steam winch with the exhaust steam line when the sleeve valve is in the closed position. Furthermore, steam chokes can be installed in the control line of the pressure control valve (pressure regulator).
In a further aspect of the invention, the sleeve valve of the pressure control valve (pressure regulator) can be loaded on one side by the working pressure of the steam winch and on the other side, instead of being loaded by the live steam pressure from the steam supply, can be loaded against the working pressure of the steam winch by means of a spring. This provides an adjustment for constant working pressure, this adjustment being independent of pressure fluctuations in the steam supply. Moreover, by changing the spring tension, this constant working pressure is infinitely adjustable to any desired magnitude. A further advantage results when the spring-applied piston side of the sleeve valve is acted upon (via an orifice) by the pressure in the exhaust steam line of the winch, since this pressure can also fluctuate in practice. By so doing, the differential pressure in the cylinders of the steam engine, which is decisive for the tension (line pull) of the winch, is adjusted to a constant value.
In an especially advantageous embodiment of the invention it is furthermore possible instead of using a separate pressure regulator, to utilize the hunting valve (which is present anyway on the steam winch) as a sleeve valve for the control of the steam pressure in such a manner that the hunting valve of the steam winch can be adjusted by means of a regulator piston which works against the force of a spring and which can be acted upon (actuated) by the working pressure of the steam winch, namely on a piston surface opposite the spring.